The Pirates have acquired shortstop John McDonald from Arizona, Ken Rosenthal reports. McDonald is owed $1.5 million in 2013, so if the Pirates are trading for him, he'll almost certainly be one of their utility infielders. He's never been able to hit at all, and at 38, there's no reason to think he'll start now, but unlike most of their other utility options (Josh Harrison, Brandon Inge, Ivan DeJesus), he's a plus defensive shortstop. The question is whether he can continue to be one at his age, but hey, Omar Vizquel was still a pretty good defender when he was 45, and McDonald isn't signed beyond 2013. One would think that Jordy Mercer could have filled the backup-shortstop role perfectly effectively, but McDonald is almost certainly the better defensive player. It's now very difficult to see Mercer making the team.
It's not yet clear what the Pirates gave up for McDonald, but I doubt strongly it's anyone interesting.
UPDATE: Jon Heyman says the Pirates gave up a player to be named, which strongly suggests it won't be anyone good.
UPDATE: The Pirates have placed Chase D'Arnaud on the 60-day DL to clear space for McDonald.
UPDATE 3:28: It's no surprise, but Neal Huntington makes it sound like McDonald is locked into one of the bench spots.